The tops of Earth's clouds dropped at least 100 feet over the course of a decade, new satellite measurements show -- a mysterious result that could be related to global warming.

Scientists who made the surprising discovery say it's too soon to tell what it means, or to make any firm link to a changing climate.

But they're already discussing one striking possibility: The lowering cloud heights might be part of a climate feedback system that could slow the planet's warming trend.

"This is the first hint we've had that can be something that slows the warming down," said Roger Davies, a professor at the University of Auckland in New Zealand. "The thing we don't know is whether the clouds are just doing their own thing, or whether they're responding to surface temperatures. If they're responding to surface temperatures in a feedback process, that could actually be quite useful."

Davies and his science team analyzed a decade's worth of data collected by an instrument aboard NASA'sTerra satellite. Called the Multi-angle Imaging SpectroRadiometer, it uses nine cameras to take stereo images of clouds across the planet.

That allows precision measurements of cloud altitude and movement, with cloud heights measured to an accuracy of 26 feet.

[caption id="attachment_168476" align="alignright" width="406" caption="Chart shows measurements by Terra satellite showing a drop in Earths cloud height of some 100 to 130 feet on average over a 10-year period. Courtesy University of Aukland/NASA/JPL/Caltech."][/caption]

The scientists found that the global average cloud height dropped about one percent between 2000 and 2010, or about 100 to 130 feet.

Most of the drop in cloud-top height came from a reduction in clouds at very high altitudes.

A reduced height in clouds would mean better cooling for the planet as it radiates heat back into space.

That could moderate the effects of global warming.

"It's unlikely to completely reverse it," Davies said. "My thinking is it would just slow it down."

But the scientists are only halfway through a 20-year project. And the data also must be weighed against many other complex climate factors, including meltic sea ice that darkens the Arctic, causing it to absorb more sunlight.

"If in another 10 years' time we get the same answer, we can start saying this is actually more likely to continue," he said.

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